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Realistic magnetic thermodynamics by local quantization of a semiclassical Heisenberg model

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npj Computational Materials 2022年第1期8卷 1771-1776页

作者： Flynn Walsh mark asta Lin-Wang Wang Materials Sciences Division Lawrence Berkeley National LaboratoryBerkeleyCA94720USA Graduate Group in Applied Science and Technology University of CaliforniaBerkeleyCA94720USA Department of Materials Science and Engineering University of CaliforniaBerkeleyCA94720USA Institute of Semiconductors Chinese Academy of Sciences100083BeijingChina

Classical Monte Carlo simulation of the Heisenberg model poorly describes many thermodynamic phenomena due to its neglect of the quantum nature of ***,we discuss how to semiclassically approach the quantum problem and demonstrate a simple method for introducing a locally approximate form of spin *** the procedure underestimates magnetic short-range order,our results suggest a simple correction for recovering realistic spin–spin correlations above the critical ***,ensemble fluctuations are found to provide reasonably accurate thermodynamics,largely reproducing quantum mechanically calculated heat capacities and experimental magnetometry for ferromagnetic Fe and antiferromagnetic *** of the method are proposed to address remaining inaccuracies.

关键词： temperature thermodynamics Heisenberg

Quantum effects on dislocation motion from ring-polymer molecular dynamics

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npj Computational Materials 2018年第1期4卷 198-203页

作者： Rodrigo Freitas mark asta Vasily V.Bulatov Department of Materials Science and Engineering University of CaliforniaBerkeleyCA 94720USA Lawrence Livermore National Laboratory LivermoreCA 94550USA Materials Sciences Division Lawrence Berkeley National LaboratoryBerkeleyCA 94720USA Department of Materials Science and Engineering Stanford UniversityStanfordCA 94305USA

Quantum motion of atoms known as zero-point vibration was recently proposed to explain a long-standing discrepancy between theoretically computed and experimentally measured low-temperature plastic strength of iron and possibly other metals with high atomic *** finding challenges the traditional notion that quantum motion of atoms is relatively unimportant in solids comprised of heavy *** we report quantum dynamic simulations of quantum effects on dislocation motion within the exact formalism of Ring-Polymer Molecular Dynamics(RPMD).To extend the reach of quantum atomistic simulations to length and time scales relevant for extended defects in materials,we implemented RPMD in the open-source code LAMMPS thus making the RPMD method widely available to the *** use our RPMD/LAMMPS approach for direct calculations of dislocation mobility and its effects on the yield strength ofα-*** simulation results establish that quantum effects are noticeable at temperatures below 50 K but account for only a modest(≈13% at T=0 K)overall reduction in the Peierls barrier,at variance with the factor of two reduction predicted earlier based on the more approximate framework of harmonic transition state *** results confirm that zero-point vibrations provide ample additional agitation for atomic motion that increases with decreasing temperature,however its enhancing effect on dislocation mobility is largely offset by an increase in the effective atom size,an effect known as quantum dispersion that has not been accounted for in the previous calculations.

关键词： theory quantum motion

Ab initio modeling of the energy landscape for screw dislocations in body-centered cubic high-entropy alloys

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npj Computational Materials 2020年第1期6卷 754-764页

作者： Sheng Yin Jun Ding mark asta Robert O.Ritchie Department of Materials Science and Engineering University of CaliforniaBerkeleyCA 94720USA Materials Sciences Division Lawrence Berkeley National LaboratoryBerkeleyCA 94720USA

In traditional body-centered cubic(bcc)metals,the core properties of screw dislocations play a critical role in plastic deformation at low ***,much attention has been focused on refractory high-entropy alloys(RHEAs),which also possess bcc crystal ***,unlike face-centered cubic high-entropy alloys(HEAs),there have been far fewer investigations into bcc HEAs,specifically on the possible effects of chemical short-range order(SRO)in these multiple principal element alloys on dislocation ***,using density functional theory,we investigate the distribution of dislocation core properties in MoNbTaW RHEAs alloys,and how they are influenced by *** average values of the core energies in the RHEA are found to be larger than those in the corresponding pure constituent bcc metals,and are relatively insensitive to the degree of ***,the presence of SRO is shown to have a large effect on narrowing the distribution of dislocation core energies and decreasing the spatial heterogeneity of dislocation core energies in the *** is argued that the consequences of the mechanical behavior of HEAs is a change in the energy landscape of the dislocations,which would likely heterogeneously inhibit their motion.

关键词： alloys deformation cubic

Modeling antiphase boundary energies of Ni_(3)Al-based alloys using automated density functional theory and machine learning

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npj Computational Materials 2022年第1期8卷 757-766页

作者： Enze Chen Artur Tamm Tao Wang Mario E.Epler mark asta Timofey Frolov Department of Materials Science and Engineering University of CaliforniaBerkeleyCA94720USA Materials Sciences Division Lawrence Berkeley National LaboratoryBerkeleyCA94720USA Materials Science Division Lawrence Livermore National LaboratoryLivermoreCA94550USA Carpenter Technology Corporation PhiladelphiaPA19103USA

Antiphase boundaries(APBs)are planar defects that play a critical role in strengthening Ni-based superalloys,and their sensitivity to alloy composition offers a flexible tuning parameter for alloy ***,we report a computational workflow to enable the development of sufficient data to train machine-learning(ML)models to automate the study of the effect of composition on the(111)APB energy in Ni_(3)Al-based *** employ ML to leverage this wealth of data and identify several physical properties that are used to build predictive models for the APB energy that achieve a cross-validation error of 0.033 J m^(−2).We demonstrate the transferability of these models by predicting APB energies in commercial ***,our use of physically motivated features such as the ordering energy and stoichiometry-based features opens the way to using existing materials properties databases to guide superalloy design strategies to maximize the APB energy.

关键词： Ni_(3)Al alloy superalloy

Spatial correlation of elastic heterogeneity tunes the deformation behavior of metallic glasses

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npj Computational Materials 2018年第1期4卷 493-502页

作者： Neng Wang Jun Ding Feng Yan mark asta Robert O.Ritchie Lin Li Department of Metallurgical and Materials Engineering The University of AlabamaTuscaloosaAL 35487USA Materials Sciences Division Lawrence Berkeley National LaboratoryBerkeleyCA 94720USA Center for Materials for Information Technology The University of AlabamaTuscaloosaAL 35487USA Department of Materials Science and Engineering University of CaliforniaBerkeleyCA 94720USA

Metallic glasses(MGs)possess remarkably high strength but often display only minimal tensile ductility due to the formation of catastrophic shear *** enhancing the inherent heterogeneity to promote distributed flow offers new possibilities in improving the ductility of monolithic ***,we report the effect of the spatial heterogeneity of elasticity,resulting from the inherently inhomogeneous amorphous structures,on the deformation behavior of MGs,specifically focusing on the ductility using multiscale modeling methods.A highly heterogeneous,Gaussian-type shear modulus distribution at the nanoscale is revealed by atomistic simulations in Cu_(64)Zr_(36) MGs,in which the soft population of the distribution exhibits a marked propensity to undergo the inelastic shear *** employing a mesoscale shear transformation zone dynamics model,we find that the organization of such nanometer-scale shear transformation events into shear-band patterns is dependent on the spatial heterogeneity of the local shear moduli.A critical spatial correlation length of elastic heterogeneity is identified for the simulated MGs to achieve the best tensile ductility,which is associated with a transition of shear-band formation mechanisms,from stress-dictated nucleation and growth to structure-dictated strain percolation,as well as a saturation of elastically soft sites participating in the plastic *** discovery is important for the fundamental understanding of the role of spatial heterogeneity in influencing the deformation behavior of *** believe that this can facilitate the design and development of new ductile monolithic MGs by a process of tuning the inherent heterogeneity to achieve enhanced ductility in these high-strength metallic alloys.

关键词： deformation ductility glasses

Theoretical prediction of high melting temperature for a Mo–Ru–Ta–W HCP multiprincipal element alloy

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npj Computational Materials 2021年第1期7卷 49-52页

作者： Qi-Jun Hong Jan Schroers Douglas Hofmann Stefano Curtarolo mark asta Axel van de Walle School of Engineering Brown UniversityProvidenceRI 02912USA Department of Mechanical Engineering and Materials Science Yale UniversityNew HavenCT 06511USA NASA Jet Propulsion Laboratory California Institute of Technology4800 Oak Grove Dr.PasadenaCA 91109USA Department of Mechanical Engineering and Materials Science and Center for Autonomous Materials Design Duke UniversityDurhamNC 27708USA Department of Materials Science and Engineering University of CaliforniaBerkeleyCA 94720USA Materials Sciences Division Lawrence Berkeley National LaboratoryBerkeleyCA 94720USA

While rhenium is an ideal material for rapid thermal cycling applications under high temperatures,such as rocket engine nozzles,its high cost limits its widespread use and prompts an exploration of viable cost-effective *** prior work,we identified a promising pool of candidate substitute alloys consisting of Mo,Ru,Ta,and *** this work we demonstrate,based on density functional theory melting temperature calculations,that one of the candidates,Mo_(0.292)Ru_(0.555)Ta_(0.031)W_(0.122),exhibits a high melting temperature(around 2626 K),thus supporting its use in high-temperature applications.

关键词： alloy cycling high

Predicting defect behavior in B2 intermetallics by merging ab initio modeling and machine learning

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npj Computational Materials 2016年第1期2卷 1-10页

作者： Bharat Medasani Anthony Gamst Hong Ding Wei Chen Kristin A Persson mark asta Andrew Canning Maciej Haranczyk Computational Research Division Lawrence Berkeley National LaboratoryBerkeleyCA 94720USA Physical and Computational Sciences Directorate Pacific National Northwest LaboratoryRichlandWA 99354USA Biostatistics and Bioinformatics University of CaliforniaSan DiegoCA 92093USA Department of Materials Science&Engineering University of CaliforniaBerkeleyCA 94720USA Energy Technologies Area Division Lawrence Berkeley National LaboratoryBerkeleyCA 94720USA Energy Technologies Area Lawrence Berkeley National LaboratoryBerkeleyCA 94720USA Department of Mechanical Materials and Aerospace EngineeringIllinois Institute of TechnologyChicagoIL 60616USA Materials Sciences Division Lawrence Berkeley National LaboratoryBerkeleyCA 94720USA

We present a combination of machine learning and high throughput calculations to predict the points defects behavior in binary intermetallic(A–B)compounds,using as an example systems with the cubic B2 crystal structure(with equiatomic AB stoichiometry).To the best of our knowledge,this work is the first application of machine learning-models for point defect *** throughput first principles density functional calculations have been employed to compute intrinsic point defect energies in 100 B2 intermetallic *** systems are classified into two groups:(i)those for which the intrinsic defects are antisites for both A and B rich compositions,and(ii)those for which vacancies are the dominant defect for either or both composition *** data was analyzed by machine learning-techniques using decision tree,and full and reduced multiple additive regression tree(MART)*** these three schemes,a reduced MART(r-MART)model using six descriptors(formation energy,minimum and difference of electron densities at the Wigner–Seitz cell boundary,atomic radius difference,maximal atomic number and maximal electronegativity)presents the highest fit(98%)and predictive(75%)*** model is used to predict the defect behavior of other B2 compounds,and it is found that 45%of the compounds considered feature vacancies as dominant defects for either A or B rich compositions(or both).The ability to predict dominant defect types is important for the modeling of thermodynamic and kinetic properties of intermetallic compounds,and the present results illustrate how this information can be derived using modern tools combining high throughput calculations and data analytics.

关键词： intermetallic intermetallics defect

An efficient and accurate framework for calculating lattice thermal conductivity of solids:AFLOW-AAPL Automatic Anharmonic Phonon Library

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npj Computational Materials 2017年第1期3卷 79-88页

作者： Jose J.Plata Pinku Nath Demet Usanmaz Jesus Carrete Cormac Toher Maarten de Jong mark asta Marco Fornari Marco Buongiorno Nardelli Stefano Curtarolo Department of Mechanical Engineering and Materials Science Duke UniversityDurhamNC 27708USA Institute of Materials Chemistry TU WienA-1060 ViennaAustria Department of Materials Science and Engineering University of CaliforniaBerkeley210 Hearst Memorial Mining BuildingBerkeleyUSA SpaceX 1 Rocket RoadHawthorneCA 90250USA Department of Physics and Science of Advanced Materials Program Central Michigan UniversityMount PleasantMI 48859USA Department of Physics and Department of Chemistry University of North TexasDentonTXUSA Materials Science Electrical EngineeringPhysics and ChemistryDuke UniversityDurhamNC 27708USA

One of the most accurate approaches for calculating lattice thermal conductivity,κ_(l),is solving the Boltzmann transport equation starting from third-order anharmonic force *** addition to the underlying approximations of ab-initio parameterization,two main challenges are associated with this path:high computational costs and lack of automation in the frameworks using this methodology,which affect the discovery rate of novel materials with ad-hoc ***,the Automatic Anharmonic Phonon Library(AAPL)is *** efficiently computes interatomic force constants by making effective use of crystal symmetry analysis,it solves the Boltzmann transport equation to obtain κ_(l),and allows a fully integrated operation with minimum user intervention,a rational addition to the current high-throughput accelerated materials development framework ***“experiment ***”study of the approach is shown,comparing accuracy and speed with respect to other available packages,and for materials characterized by strong electron localization and *** AAPL with the pseudo-hybrid functional ACBN0 is possible to improve accuracy without increasing computational requirements.

关键词： properties. harmonic calculating

Real time imaging of two-dimensional iron oxide spherulite nanostructure formation

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Nano Research 2019年第11期12卷 2889-2893页

作者： Wenjing Zheng Matthew R.Hauwiller Wen-I Liang Colin Ophus Peter Ercius Emory M.Chan Ying-Hao Chu mark asta Xiwen Du A.Paul Alivisatos Haimei Zheng Institute of New-Energy Materials School of Materials Science and EngineeringTianjin UniversityTianjin300350China Materials Sciences Division Lawrence Berkeley National LaboratoryBerkeleyCA94720USA Department of Chemistry University of CaliforniaBerkeleyBerkeleyCA94720USA Department of Materials Science and Engineering “National Chiao Tung University”Hsinchu30010TaiwanChina The Molecular Foundry Lawrence Berkeley National LaboratoryBerkeleyCA94720USA Department of Materials Science and Engineering University of CaliforniaBerkeleyBerkeleyCA94720USA Kavli Energy NanoScience Institute University of California-Berkeley and Lawrence Berkeley National LaboratoryBerkeleyCA94720USA

The formation of complex hierarchical nanostructures has attracted a lot of attention from both the fundamental science and potential applications point of *** structures with radial fibrillar branches have been found in various solids;however,their growth mechanisms remain poorly ***,we report real time imaging of the formation of two-dimensional(2D)iron oxide spherulite nanostructures in a liquid cell using transmission electron microscopy(TEM).By tracking the growth trajectories,we show the characteristics of the reaction front and growth *** observations reveal that the tip of a growing branch splits as the width exceeds certain sizes(5.5–8.5 nm).The radius of a spherulite nanostructure increases linearly with time at the early stage,transitioning to nonlinear growth at the later ***,a thin layer of solid is accumulated at the tip and nanoparticles from secondary nucleation also appear at the growing front which later develop into fibrillar *** spherulite nanostructure is polycrystalline with the co-existence of ferrihydrite and Fe3O4 through-out the growth.A growth model is further established,which provides rational explanations on the linear growth at the early stage and the nonlinearity at the later stage of growth.

关键词： liquid cell transmission electron microscopy(TEM) in situ TEM iron oxide spherulite nanostructures